Found 23 talks width keyword high-redshift galaxies

Abstract

Thanks to its unique capabilities, the MUSE integral field spectrograph at ESO VLT has given us new insight of the Universe at high redshift. In this talk I will review some breakthrough in the observation of the Hubble Ultra Deep field with MUSE including the discovery of a new population of faint galaxies without HST counterpart in the UDF and the ubiquitous presence of extended Lyman-alpha haloes around galaxies.

Abstract

There are galaxies that remain untouched since the ancient Universe. These unique objects, the so-called relic galaxies, are several times more massive than our Milky Way but with much smaller sizes, and containing very old (>10 Gyr) stellar populations. For the very few of them already found and analysed (most of them by our IAC colleagues), they seem to host "too heavy" central super massive black holes, also displaying an overabundance of low mass versus high mass stars and retaining their primeval morphologies and kinematics. How did they survive until the present day? Simulations predict that they reside in galaxy overdensities whose large internal random motions prevent galaxies from merging. However, we have not yet determined observationally neither the environments these galaxies inhabit nor how many there are (their number densities). We make use of the GAMA survey, that allows us to conduct a complete census of this elusive galaxy population, because of its large area and spectroscopic completeness. After inspecting 180 square degrees of the sky using the deepest photometric images available, we identified 29 massive ultracompact galaxies in the nearby Universe (0.02 < z < 0.3), that are true windows to the ancient Universe. I will present the first paper about this exceptional sample, describing their properties andhighlighting the fact that while some galaxies seem to be satellitesof bigger objects, others are not located in clusters, at odds with the theoretical expectations.

Abstract

Models of galaxy formation predict that gas accretion from the cosmic web is a primary driver of star formation over cosmic history. Except in very dense environments where galaxy mergers are also important, model galaxies feed from cold streams of gas from the web that penetrate their dark matter haloes. Although these predictions are unambiguous, the observational support has been indirect so far. I will report spectroscopic evidence for this process in extremely metal-poor galaxies (XMPs) of the local Universe, taking the form of localized starbursts associated with gas having low metallicity. Because gas mixes azimuthally in a rotation timescale (a few hundred Myr), the observed metallicity inhomogeneities are only possible if the metal-poor gas producing stars fell onto the disk recently. I will analyze several possibilities for the origin of the metal-poor gas, favoring the metal-poor gas infall predicted by numerical models. In addition, I will show model galaxies in cosmological numerical simulations with starbursts of low metallicity like to the star-forming regions in XMPs.

Abstract

Almost all cosmologists accept nowadays that the redshift of the galaxies is due to the expansion of the Universe (cosmological redshift), plus some Doppler effect of peculiar motions, but can we be sure of this fact by means of some other independent cosmological test? Here I will review some recent tests: CMBR temperature versus redshift, time dilation, the Hubble diagram, the Tolman or surface brightness test, the angular size test, the UV surface brightness limit and the Alcock-Paczynski test. Some tests favour expansion and others favour a static Universe. Almost all the cosmological tests are susceptible to the evolution of galaxies and/or other effects. Tolman or angular size tests need to assume very strong evolution of galaxy sizes to fit the data with the standard cosmology, whereas the Alcock-Paczynski test, an evaluation of the ratio of observed angular size to radial/redshift size, is independent of it.

Abstract

The importance of Luminous and Ultraluminous infrared galaxies (U/LIRGs) in the context of the cosmological evolution of the star-formation has been well established in the last decades. They have been detected in large numbers at high-z (z>1) in deep surveys with Spitzer and Herschel, and they seem to be the dominant component to the star formation rate (SFR) density of the Universe beyond z~2. Although rare locally, nearby U/LIRGs are valuable candidates to study extreme cases of compact star-formation and coeval AGN. In particular, the study of local U/LIRGs using near-IR integral field spectroscopic techniques allows us to disentangle the 2D distribution of the gas and the star-formation using high spatial resolution, and characterise dust-enshrouded, spatially-resolved star-forming regions with great amount of detail. In that context, we are carrying on a comprehensive 2D IFS near-IR survey of local 10 LIRGs and 12 ULIRGs, based on VLT-SINFONI observations. I will review different topics on the spatially resolved study of the ISM and the star-formation at different spatial scales. I will focus on the analysis of the multi-phase gas morphology and kinematics, and on the study of the spatially-resolved distribution of the extinction-corrected star-formation rate (SFR) and star-formation rate surface density (ΣSFR). In particular, I will present some recent results on the characterization of individual star-forming regions, in terms of their sizes and Paα luminosities.

Abstract

Our Universe is filled with a mind-blowing diversity and different types and appearances of galaxies. Finding out about how they formed and evolved is one of the most challenging tasks in astronomy. When looking about 10 billion years back, to an epoch about 3 billion years after the big bang, we can see galaxies at earlier stages of their lives. In this talk, studies of different kinds of galaxies in the early universe will be presented. Two examples of the very intriguing population of massive quiescent z~2 galaxies were analyzed in terms of their stellar populations and morphologies. As the spectroscopic sample is still small, especially for galaxies at the faint end of the luminosity function, we make use of the biggest available "telescopes" in the universe: We search for red z~2 galaxies whose apparent brightnesses have been boosted by the Gravitational Lensing effect of intermediate redshift galaxy clusters with available mass models. Our findings indicate older ages for these galaxies than expected. Also, their remarkable compactness was corroborated. Furthermore, I'm going to present a study of a special case of so-called Damped Lyman-alpha Absorbers (DLAs), with two intervening galaxies in the line of sight of a higher-redshift QSO, which is also one example of only about a dozen known galaxy counterparts of a DLA. It fits into the emerging paradigm that galaxies which are responsible for higher metallicity DLAs are more massive and luminous than typical DLA galaxies. Motivated by that particular discovery, during the past few years we have undertaken a survey targeting candidate dust-reddened quasars missing in the sample from Sloan Digital Sky Survey. Spectroscopic follow-up with the NOT and the NTT has demonstrated a very high success rate of our selection (>90%). The main motivation is to search for quasars reddened by foreground dusty galaxies and we have found several such examples. We have also serendipitously found quasars with abnormal, very UV-steep extinction curves as well as a large number of broad absorption line quasars (BALs). The latter allow us to study the dependence of the BAL QSO population on redshift, reddening and luminosity. The results show a strong evolution of the BAL QSO fraction with cosmic time, with a peak at z~2.5 where several quantities in the Universe are also found to peak or vary. In addition,the dependence of this fraction with reddening and luminosity provides new constraints on the models for broad absorption origin in quasars. We are currently carrying out a pilot study of a search for even redder quasars selected from a combination of SDSS, UKIDSS and WISE photometry with the aim of selecting very dust-obscurred quasars or high-redshift BALs at z>2. Preliminary results from the first run et the NOT in March 2015 of the brightest candidates show very promising results which will also be briefly shown in the talk.

Abstract

Over the past ~20 years the high-redshift Universe has been increasingly opened to scrutiny at far-infrared wavelengths, where cool dust emission from star-formation dominates. The dusty star-forming galaxies (DSFGs) and submillimeter galaxies (SMGs), selected at these wavelengths likely represent an important, but short-lived phase in the growth of massive galaxies. These DSFGs often have star-formation rates in excess of ~1000 solar masses per year and are confirmed out to at least z~6, although their redshifts and high dust contents make them faint and difficult to study at other wavelengths. Now, using data from the Herschel Space Observatory we have identified a population of DSFGs that are strongly gravitationally lensed and therefore magnified and available for unprecedented multi-wavelength scrutiny. I will describe how this important gravitationally lensed population is identified, and present and interpret the data from our extensive multi-wavelength, multi-facility follow-up studies. I will also present follow-up observations of an intriguing sample of the highest redshift DSFGs (z>4) that are also selected via Herschel data, and that are proving troublesome to explain in galaxy formation simulations.

Abstract

One of the most widely researched topics in Extragalactic Astrophysics in the last decades is how early-type galaxies have formed their stars and assembled. In this context, we now have unequivocal observational evidences about the existence of a numerous population of massive galaxies which not only had assembled a considerable amount of stars (~10^11 M_sun) by z~2, but were already evolving passively by that time. These galaxies, the likely progenitors of nearby ellipticals, are also quite compact in comparison with local galaxies of the same mass. These result are mainly based on measurements designed to obtain stellar masses and sizes, and our estimations of these parameters are now quite robust. Now we need a more secure determination of how exactly they formed and assembled their stellar mass in just 2-3 Gyr (z>2). In other words, how was their Star Formation History and which are the properties (age, metallicity, dust content) of their stellar populations? And how could they end up with such high masses and small sizes? In this talk, we will present our results about the SFH (mainly ages and duty cycles) of massive galaxies at z=1-3 based on the deepest spectro-photometric data ever taken. These data were gathered by the Survey for High-z Absorption Red and Dead Sources (SHARDS), a ESO/GTC Large Program aimed at obtaining R~50 optical spectra of distant galaxies. This resolution is especially suited to measure absorption indices such as D(4000), Mg_UV, the Balmer break,etc.. for galaxies up to z~3 (merging our SHARDS data with HST/WFC3 grism observations) or emission-line fluxes for faint targets up to z~6. These measurements represent a big step forward for the robust determination of the stellar population properties, providing a much more certain characterization of the stellar content of distant galaxies than the typical broad-band studies. Our results uniquely allow to study the stellar content of red and dead galaxies at z~2 and identify progenitors at higher redshifts, as well as helping to constrain the models of galaxy formation.

Abstract

The first galaxies are thought to have started the reionization of the Universe, that is the transformation of the cosmic hydrogen from its initial neutral to its present ionized state that occurred during the first few hundred million years after the Big Bang. I will review the key physics of reionization by the first galaxies and highlight the computational challenges of simulating the relevant processes, primarily the transport of ionizing photons. I will introduce the radiative transfer method TRAPHIC that we have developed to address these challenges. I will discuss the application of TRAPHIC in zoomed cosmological simulations of the first galaxies and evaluate the prospects for observing these galaxies with the upcoming James Webb Space Telescope. I will conclude by presenting first results from Aurora, a new suite of simulations to investigate reionization and galaxy formation across a large range of scales.

Abstract

DESI is a massively multiplexed fiber-fed spectrograph that will make the nextmajor advance in dark energy in the timeframe 2018-2022. On the Mayalltelescope, DESI will obtain spectra and redshifts for tens of millions ofgalaxies and cuasars with 5,000 fiber postioner robots, constructing a3-dimensional map spanning the nearby universe to 10 billion light years. DESIis supported by the US Department of Energy Office of Science to perform thisStage IV dark energy measurement using baryon acoustic oscillations and othertechniques that rely on spectroscopic measurements. Spain has a major role inDESI with the construction of the Focal Plate and the development of the fiberpositioners. I will give an overview of the DESI science, instrument, and Spainparticipation in the project.